Memory devices can be broadly categorized into two classes: volatile memory and non-volatile memory. Volatile memory (e.g., SRAM, DRAM, or the like) lose their data content when the power supply is removed. In contrast, non-volatile memories (e.g., EEPROM, flash memories, or the like) maintain their data content after the power supply has been removed.
Flash memory is a non-voltage memory that can be electrically erased and reprogrammed. One common type of flash memory device is charge-trap (CT) flash memory. The basic concept of a charge-trap flash memory cell is that of a CT layer in a semiconductor transistor. The electrical isolation of the CT layer is accomplished by surrounding it with dielectric material, such as an oxide. Typically, charge trap flash memory cells use two oxide layers, a “bottom” oxide layer and a “top” oxide layer.